Quantitative analysis of the native presynaptic cytomatrix by cryoelectron tomography

The presynaptic terminal contains a complex network of filaments whose precise organization and functions are not yet understood. The cryoelectron tomography experiments reported in this study indicate that these structures play a prominent role in synaptic vesicle release. Docked synaptic vesicles did not make membrane to membrane contact with the active zone but were instead linked to it by tethers of different length. Our observations are consistent with an exocytosis model in which vesicles are first anchored by long (>5 nm) tethers that give way to multiple short tethers once vesicles enter the readily releasable pool. The formation of short tethers was inhibited by tetanus toxin, indicating that it depends on soluble N-ethyl-maleimide sensitive fusion protein attachment protein receptor complex assembly. Vesicles were extensively interlinked via a set of connectors that underwent profound rearrangements upon synaptic stimulation and okadaic acid treatment, suggesting a role of these connectors in synaptic vesicle mobilization and neurotransmitter release.

The supramolecular assemblies of voltage-dependent anion channels in the native membrane

Voltage-dependent anion channels (VDACs) are major constituents of the outer mitochondrial membrane (OMM). These primary transporters of nucleotides, ions and metabolites mediate a substantial portion of the OMM molecular traffic. To study the native supramolecular organization of the VDAC, we have isolated, characterized and imaged OMMs from potato tubers. SDS-PAGE and mass spectrometry of OMMs revealed the presence of the VDAC isoforms POM34 and POM36, as well as the translocase of the OMM complex. Tubular two-dimensional crystals of the VDAC spontaneously formed after incubation of OMMs for two to three months at 4 degrees C. Transmission electron microscopy revealed an oblique lattice and unit cells housing six circular depressions arranged in a hexagon. Atomic force microscopy of freshly isolated OMMs demonstrated (i) the existence of monomers to tetramers, hexamers and higher oligomers of the VDAC and (ii) its spatial arrangement within the oligomers in the native membrane. We discuss the importance of the observed oligomerization for modulation of the VDAC function, for the binding of hexokinase and creatine kinase to the OMM and for mitochondria-mediated apoptosis.

Human-environment interactions in pre-Columbian Amazonia: The case of the Llanos de Moxos, Bolivia

The reconstruction of past environmental and historical events is much needed in Amazonia, a region at the centre of heated debates about the extent of pre-Columbian human disturbance of the natural ecosystems. Important aspects of this debate are to establish to what extent the rise of social complexity was influenced by the local geo-ecology; and what productive strategies were adopted in order to sustain these societies. The Llanos de Moxos (LM), in the Bolivian Amazon, is a vast floodplain made up of a variety of geo-ecological sub regions that host many different types of pre-Columbian earthworks. Therefore, it offers an excellent opportunity to compare different kinds of archaeological landscapes and their relationship to different pre-Columbian cultures and environmental settings. This paper analyses the links between pre-Columbian earthworks and the local geo-ecology in two regions of the LM: 1) the platform field region (PFR) in the north of Santa Ana de Yacuma, where the highest concentration of raised fields has been documented, and 2) the monumental mounds region (MMR) south and east of Trinidad, where >100 pre-Columbian monumental mounds are found. The study draws from remote sensing and GIS analysis, field work in the Bolivian lowlands, and laboratory analysis. Differences in the way people transformed the landscape in the PFR and MMR seem to respond to differences in the local geo-ecology of the two sites. The results also suggest that environmental conditions exerted an important, though not exclusive, control over the levels of social complexity that were reached in different areas of the LM.

Non-naturalized alien plants receive fewer flower visits than naturalized and native plants in a Swiss botanical garden

Many animal-pollinated plant species have been introduced to non-native regions without their usual pollinators. Nevertheless, some of these alien species managed to establish reproducing naturalized populations, which might negatively affect native plants. Recent studies have shown that many naturalized alien species can readily attract native pollinators. However, it is not known whether alien species that have not established naturalized populations are less successful in attracting pollinators. Therefore, we tested whether flower-visitation rates are lower for non-naturalized aliens than for naturalized alien and native species. We conducted a comparative study on flower visitation of 185 native, 37 naturalized alien and 224 non-naturalized alien plant species in the Botanical Garden of Bern, Switzerland. Our phylogenetically corrected analyses showed that non-naturalized alien species received fewer flower visitors than both naturalized alien and native species. Native, naturalized alien and non-naturalized alien species were visited by similar flower-visitor communities. Furthermore, among the naturalized alien species, the ones with a broader distribution range in Switzerland received a more diverse set of flower visitors. Although it has been suggested that most alien plants can readily integrate into native plant–pollinator networks, we show evidence that the capacity to attract flower visitors in non-native regions is different for naturalized and non-naturalized alien plants. Therefore, we conclude that successful naturalization of alien plants may be related to flower visitation.